Control of the transmission power represents an important performance feature in mobile radio systems in order to suppress possible interference between the individual connections and, thus, to make it possible to improve the capacity and quality of the connections, in order to be able to reduce the mean transmission power and to be able to match it as well as possible to the requirements, as well as to make it possible to compensate, at least partially, for losses in the transmission channels.
For this purpose, the signal transmitted by a transmitter is evaluated at the receiving end in the mobile radio system, in order to make it possible for this to produce information for power control and to transmit this to the transmitter, which then adjusts the transmission power in accordance with the power control or power adjustment information.
In this case, the power adjustment information is transmitted analogously to the transmission of the actual communication information, depending on the respective mobile radio system, embedded in a predetermined frame and timeslot structure; that is to say, the information is transmitted in a number of sequentially transmitted frames, with each frame having a specific number of timeslots. For known mobile radio systems, it has been proposed for the transmitter of the mobile radio system to be operated in a mode which is referred to as the slotted mode or compressed mode, with the information to be transmitted in this case being transmitted within specific frames in compressed form to a receiver in order to make it possible, in the appropriate frame, to produce a section which is free of information bits, and which is referred to as an idle slot, which can then be used for intermediate frequency measurements; for example, in order to prepare for a handover between different mobile radio systems. The information must be transmitted in a shorter time interval for compression.
The principle of compression is illustrated schematically in FIG. 4, with a number of sequentially transmitted frames 3 being shown, each of which has an identical frame duration; for example, 10 ms. The second frame 3 shown in FIG. 4 uses the slotted mode, that is to say the information is transmitted in compressed form in this frame, so that an idle slot 9 occurs in which information is now transmitted. As is likewise shown in FIG. 4, the transmission power can be increased during this frame 3 that is operated in the slotted mode in order to achieve a transmission quality which is not adversely affected by the slotted mode.
However, the slotted mode interrupts the principle of fast power control. In modern mobile radio systems, power adjustment information for the transmitter is produced in each timeslot so that the transmission power can be adapted relatively quickly. However, no such power adjustment information can be transmitted during the idle slots described above. Firstly, this results in a higher error rate for the power adjustment information bits and, secondly, it must be expected that the instantaneous transmission power will deviate to a greater extent from the nominal value.
In order to overcome this problem associated with the slotted mode, it has been proposed, for example, to temporally increase the energy in what are referred to as pilot bits after the slotted mode, for power control, in order to allow correct decoding of the power adjustment information which is generally formed only by a corresponding bit with a specific mathematical sign. The pilot bits are used to estimate the channel impulse response during what is referred to as a training sequence, and they correspond to a known bit pattern. The power control procedure for the slotted mode as described in this document is, however, relatively complicated and requires a relatively large amount of effort.
The present invention is, thus, directed toward an improved method for controlling the transmission power in a radio system, and a corresponding radio system, in which case the aim is to reliably control the transmission power, particularly, in the slotted mode or compressed mode described above.